ABSTRACT Oxygenation state of the wound tissue is known to influence wound outcomes by a number of mechanisms ranging from enabling oxidative metabolism, fighting infection, hydroxylating collagen, generating nitric oxide, and generating reactive oxygen species which may support redox signaling. The etiology of chronic ischemic wounds is generally multi-factorial of which hypoxia caused by underlying peripheral vasculopathy is a common factor. Hypoxia is generally viewed as being angiogenic. So why does the ischemic wound not close even faster? Although hypoxia may have favorable effects on endothelial cells, the hypoxia-inducible transcription factor HIF specifically induces growth arrest of keratinocytes compromising wound closure. HIF1 is abundant in basal keratinocytes at the wound edge and causes growth arrest. Our observation directly implicates hypoxia-inducible microRNA (miRNA) or hypoxamir in arresting keratinocyte function. Specifically, we noted that the hypoxamir miR-210 silences target genes which would arrest growth/migration as well as repress mitochondrial metabolism in keratinocytes. In both mice and chronic wound patients, ischemic wounds showed elevated miR-210 levels. Next, we screened for miR-210 dependent pathways that would impair wound re-epithelialization. We studied the candidate pathways that emerged from murine studies for their relevance to human chronic wounds. Those specific pathways that emerged from murine studies and were successfully validated using human chronic wound-edge tissue were selected for study in this proposal. microRNA (miR or miRNA) represents a class of recently discovered non-coding (nc) genes that are of such extraordinary significance in human health and disease. Whether a set of coding gene would be functional or silenced is decided by specific miRs targeting that set of genes. As we seek to take the study of tissue oxygenation and wound healing to the future, we have chosen to focus on unveiling the significance of hypoxamir miR-210 in regulating wound closure. Three aims are proposed: Aim 1: Characterize mechanisms underlying miR-210 dependent compromised wound re-epithelialization of ischemic wounds. 1.1 Ischemic wound-associated elevation of miR-210 silences ISCU1/2 inhibiting mitochondrial metabolism; 1.2 Elevated miR-210 silences E2F3 causing p53 activation and inhibition of keratinocyte proliferation; 1.3 miR-210 up-regulation silences ACVR1B impeding keratinocyte migration. Aim 2: Determine molecular mechanisms underlying induction of miR-210 by ischemia; Central hypothesis: Wound ischemia induces keratinocyte miR-210 via HIF1 and lactate. 2.1 HIF-1/ARNT and novel co- activators drive hypoxia-induced miR-210 expression; 2.2 Lactate drives miR-210 expression. Aim 3: Elevated miR-210 in the epidermis of ischemic human wound edge tissue is associated with poor healing outcome in a setting of standard clinical care. We propose a prospective longitudinal study where adult non-diabetic patients with chronic leg ulcers visiting the OSU Comprehensive Wound Center will be enrolled.